Author and year
(Country)
|
Type of Study and level of evidence
|
Sample
|
CR Indicator
|
Results
|
Cotrena et al. 2017
(Brazil)
|
Cross-sectional
*Level 4
|
38 patients with bipolar I disorder, 39 with bipolar II disorder, and 106 healthy controls
|
Reading and writing habits, IQ (the block design and vocabulary subtest from WAIS-III)
|
Reading and writing habits, IQ, and frequency of diagnosis predicted suppression control. IQ and diagnostic frequency predicted working memory. Cognitive flexibility was predicted by reading and writing.
|
Cotrena et al. 2020
(Brazil)
|
Cross-sectional
*Level 4
|
95 patients with bipolar disorder and 103 adults with no mood disorder
|
IQ (the block design and vocabulary subtest from WAIS-III) and years of formal education
|
People with bipolar disorder had lower executive function and functional levels than controls. IQ mediated cognitive function and affected functional levels.
|
Donaldson et al. 2003
(England)
|
Case control
*Level 4
|
43 patients with bipolar I disorder
|
Full scale IQ (WAIS-III)
|
Low IQ in childhood may not be associated with the development of bipolar type I disorder.
|
Drakopoulos et al. 2020
(Sweden)
|
Longitudinal (cohort)
*Level 2
|
120 patients with bipolar disorder
|
Full scale IQ (WAIS-III) and occupational functioning (work of studying)
|
Univariate analyses revealed better overall cognitive function in active patients in terms of IQ and executive functioning.
|
Forcada et al. 2015
(Spain)
|
Cross-sectional
*Level 4
|
52 patients with bipolar disorder and 49 healthy controls
|
Education-occupation, leisure activities, and premorbid IQ
|
Euthymic patients with bipolar disorder had lower executive function, verbal, and visual memory performance than healthy controls. CR predicted cognitive and functional outcomes.
|
Fuentes et al. 2016
(Mexico)
|
Cross-sectional
*Level 4
|
34 patients with bipolar disorder (12 with low compliance to the treatment and 22 with high compliance)
|
Years of education
|
Patients with low level of compliance performed significantly worse than those with high treatment compliance on various memory tests. Years of education was an important factor for executive function and processing speed.
|
Gale et al. 2013
(Sweden)
|
Cross-sectional
*Level 4
|
60 patients with bipolar disorder and 60 healthy controls
|
Verbal IQ (a reading test) and non-verbal IQ (a progressive matrices test)
|
Despite comparable IQ levels, patients with bipolar disorder completed fewer years of education than controls.
|
Garcia-Laredo et al. 2015
(Spain)
|
Cross-sectional
*Level 4
|
24 patients with bipolar disorder and 15 healthy controls
|
Years of education
|
There was no difference between the groups in terms of verbal fluency performance. Years of education impacted semantic verbal fluency and correlated with phonemic verbal fluency.
|
Gilbert et al. 2010
(USA)
|
Longitudinal (cohort, 15–43 months of follow-up)
*Level 2
|
154 patients with bipolar I disorder
|
Years of education
|
Baseline concentration problems and years of education significantly predicted employment.
|
Glahn et al. 2006
(USA)
|
Longitudinal (cohort, 22.6 years of follow-up)
|
1,049,607 Swedish man.
|
IQ was measured at a mean age of 18.3 years using four written subtests of verbal, logical, spatial, and technical ability.
|
Compared to men with average verbal ability, risk of hospitalization with pure bipolar disorder rose as verbal ability increased, such that men with the highest verbal ability had a 41% increase in risk; men with the lowest verbal ability had an increase in risk of 34%.
|
Hinrichs et al. 2017
(UAS)
|
Longitudinal (cohort, five years of follow-up)
*Level 2
|
1,059 patients with bipolar disorder and 54 healthy controls
|
CR (verbal IQ and years of education)
|
The overall relative rate of change in cognitive function did not differ between the bipolar disorder and healthy control groups. Intellectual ability may be a protective factor against cognitive decline.
|
Jimenez et al. 2017
(Spain)
|
Cross-sectional
*Level 4
|
113 patients with bipolar disorder
|
The estimated IQ (the vocabulary subtest from the WAIS-III)
|
A higher estimated IQ may act as a protective factor against cognitive decline in this group of patients.
|
Koenen et al. 2009
(UK)
|
Longitudinal (cohort, 32 years of follow-up)
*Level 2
|
1,037 healthy children
|
IQ (WISC-R)
|
Higher childhood IQ predicted increased risk of adult mania.
|
Lima et al. 2019
(Brazil)
|
Case-control
*Level 4
|
Of bipolar disorder, 30 with intact cognition, 23 with selective cognitive impairment, and 16 with global cognitive impairment
|
The estimated IQ (the vocabulary and matrix reasoning subtest from WAIS-III) and Years of education
|
The intact group had more years of education and a higher estimated IQ than globally and selectively impaired subgroups of patients with bipolar disorder.
|
Lin et al. 2020
(China)
|
Cross-sectional
*Level 4
|
125 bipolar I disorder and 60 healthy controls
|
Premorbid intelligence (the vocabulary subtest from the WAIS-R) and educational level (total years of education completed)
|
Premorbid intelligence significantly moderated the associations between the number of bipolar episodes and neurocognitive functioning, and the educational level also moderated the relationships between the total number of bipolar episodes and subjective cognitive functioning.
|
Levy et al. 2011
(USA)
|
Longitudinal (cohort, three months of follow-up)
*Level 3
|
82 patients with bipolar disorder
|
The estimated IQ (WAIS vocabulary and block design subtest), years of education and employment
|
Significant group differences emerged on the measure of IQ. There was no difference in years of education and employment between those with bipolar disorder, whose remission was maintained, and those who relapsed at three months of follow-up.
|
Martino et al. 2017
(Argentina)
|
Cross-sectional
*Level 4
|
119 patients with bipolar disorder and 40 healthy controls
|
Premorbid IQ (the WAIS vocabulary subset)
|
Premorbid IQ might moderate the relationship between the number of hypo/manic episodes and executive function.
|
Martino et al. 2008
(Argentina)
|
Cross-sectional
*Level 4
|
50 patients with bipolar disorder and 30 healthy controls
|
Premorbid IQ (the WAIS vocabulary subset)
|
Patients with cognitive functioning within normal limits had higher psychosocial functioning and premorbid IQ.
|
Posoni et al. 2020
|
Cross-sectional
*Level 4
|
111 patients with bipolar disorder and 91 patients with major depressive disorder
|
CR scores calculated by principal component analysis of the estimated IQ (the vocabulary and block design subtests in WAIS-III), years of education, and frequency of reading and writing
|
CR may be protective against cognitive impairment in patients with bipolar disorder.
|
Tabarés-Seisdedos, et al. 2008 (Spain)
|
Longitudinal (cohort, one-year of follow-up)
*Level 3
|
43 patients with bipolar disorder, 25 healthy controls
|
The estimated premorbid IQ (the vocabulary subtest of the WAIS-R) and years of education
|
Executive function, attention, and working memory were lower in those with bipolar disorder than in healthy subjects at the time of one year follow-up. Years of education and estimated IQ did not explain occupational adaptation, but executive function and reasoning ability did.
|
Tsapekos et al. 2020
(UK)
|
Cross-sectional
*Level 4
|
80 patients with bipolar disorder: 25 cognitively intact; 15 selective deficits in verbal learning and memory; 30 intermediate deficits across all cognitive domains; 10 severe deficits across all domains
|
CR estimated three proxy measures: years of education and two premorbid intelligence scales (the vocabulary subtest in WAIS-III and the test of premorbid function)
|
Cognitive functioning decline after the onset of bipolar symptoms was most pronounced in severe cases, with the lowest cognitive reserve.
|
Strassning et al. 2018
(USA)
|
Longitudinal (cohort, 20 years of follow-up)
*Level 2
|
87 patients with bipolar disorder: 46 employed; 41 non-employed)
|
Occupation (interview of gainful employment)
|
Patients with bipolar disorder who had full-time employment had a negative correlation with depressive symptoms. Employment was positively correlated with cognitive test performance.
|
Romero et al. 2016
(Argentina)
|
Cross-sectional
*Level 4
|
46 patients with bipolar II disorder and 46 healthy controls
|
The premorbid IQ (vocabulary subtest in WAIS-III)
|
Significant correlations were identified in bipolar patients regarding hyperthymic temperament, verbal memory, and premorbid IQ.
|
Ryan et al. 2013
(USA)
|
Cross-sectional
*Level 4
|
156 patients with bipolar disorder and 143 healthy controls
|
Occupation using the DIGS and the premorbid IQ (vocabulary subtest in WAIS-III)
|
Patients with bipolar disorder who were unemployed/unable to work exhibited greater difficulties processing emotional information and on executive function as compared to those who were employed, independent of other factors. The premorbid IQ may not be relevant to getting a responsible job.
|